Decomposition of Dioxins in Fly Ash by Hydrothermal Treatment

概要

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In order to reduce the toxicity of Municipal Solid Waste Incinerator (MSWI) fly ash containing polychlorinated dibenzodioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs), well-known as highly toxic organic pollutants, fly ash was hydrothermally treated. Under hydrothermal conditions, concentration of PCDDs and PCDFs decreased due to dechlorination reaction. This reaction occurred more effectively with high temperature and the existence of alkaline ingredients and/or methanol in solvent. Even at 373 K, which is relatively lower than the operating temperatures of thermal decomposition technique, the dechlorination reaction took place. PCDDs/PCDFs decomposed almost completely and toxicity of treated ash decreased to 0.03ng-TEQ/g at 573 K for 20 min with the solvent of 1 N NaOH solution and methanol. Estimated activated energy for the reaction, assuming that the whole of PCDDs/ PCDFs was one chemical species, was about 13 kcal/mol and reaction rate constant k was expressed as k=2.27×104exp {-13.2/ (RT) } .
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